Last time the littlies and I did "science tricks" together we noticed the gas (carbon dioxide) given off when you mix an acid (vinegar) and a base (calcium carbonate/sodium bicarbonate). The kids were dead keen to do the baking soda/vinegar trick again. "Sure" I said "But shall we see what this reaction tastes like? We could make bubbles on our tongues!"
"...Okay..." they replied, in timid voices. I trotted off to the cupboard and brought back the ingredients for sherbet.
Mix together: 1/2 t citric acid, 1/4 t baking soda, and 3 t icing sugar. Grind them up in a mortar and pestle if you have one. Make sure they stay nice and dry.
Now put a little in a glass and get a straw. Suck a little up onto your tongue and feel it fizzing as the acid (citric acid) reacts with the base (baking soda). This is the taste of a real-life chemical reaction on your tongue. The acid will taste sour and tangy, and the sugar will be nice and sweet. There's also a rather scintillating cold feeling- that's because this reaction is endothermic (it absorbs heat to break the chemical bonds).
Harry thought that adding water might make it into a fizzy drink. We tried it out. It fizzed alright, but the bubbles were gone by the time he drank it. (This showed him that the reaction is instantaneous).
Sylvie thought that the flavour could be improved. We talked about other things we could put in to make a different flavour: powdered fruit drink, jelly crystals, different types of sugar. Whatever flavour you choose, it must be dry, because the reaction happens as soon as you add water.